text: /*
   * bitstream
   * Part of FSE library
   * header file (to include)
   * Copyright (C) 2013-2016, Yann Collet.
   *
   * BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   *
   *   * Redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer.
   *   * Redistributions in binary form must reproduce the above
   * copyright notice, this list of conditions and the following disclaimer
   * in the documentation and/or other materials provided with the
   * distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * This program is free software; you can redistribute it and/or modify it under
   * the terms of the GNU General Public License version 2 as published by the
   * Free Software Foundation. This program is dual-licensed; you may select
   * either version 2 of the GNU General Public License ("GPL") or BSD license
   * ("BSD").
   *
   * You can contact the author at :
   * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
   */
  #ifndef BITSTREAM_H_MODULE
  #define BITSTREAM_H_MODULE
  
  /*
  *  This API consists of small unitary functions, which must be inlined for best performance.
  *  Since link-time-optimization is not available for all compilers,
  *  these functions are defined into a .h to be included.
  */
  
  /*-****************************************
  *  Dependencies
  ******************************************/
  #include "error_private.h" /* error codes and messages */
  #include "mem.h"	   /* unaligned access routines */
  
  /*=========================================
  *  Target specific
  =========================================*/
  #define STREAM_ACCUMULATOR_MIN_32 25
  #define STREAM_ACCUMULATOR_MIN_64 57
  #define STREAM_ACCUMULATOR_MIN ((U32)(ZSTD_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64))
  
  /*-******************************************
  *  bitStream encoding API (write forward)
  ********************************************/
  /* bitStream can mix input from multiple sources.
  *  A critical property of these streams is that they encode and decode in **reverse** direction.
  *  So the first bit sequence you add will be the last to be read, like a LIFO stack.
  */
  typedef struct {
  	size_t bitContainer;
  	int bitPos;
  	char *startPtr;
  	char *ptr;
  	char *endPtr;
  } BIT_CStream_t;
  
  ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *dstBuffer, size_t dstCapacity);
  ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
  ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC);
  ZSTD_STATIC size_t BIT_closeCStream(BIT_CStream_t *bitC);
  
  /* Start with initCStream, providing the size of buffer to write into.
  *  bitStream will never write outside of this buffer.
  *  `dstCapacity` must be >= sizeof(bitD->bitContainer), otherwise @return will be an error code.
  *
  *  bits are first added to a local register.
  *  Local register is size_t, hence 64-bits on 64-bits systems, or 32-bits on 32-bits systems.
  *  Writing data into memory is an explicit operation, performed by the flushBits function.
  *  Hence keep track how many bits are potentially stored into local register to avoid register overflow.
  *  After a flushBits, a maximum of 7 bits might still be stored into local register.
  *
  *  Avoid storing elements of more than 24 bits if you want compatibility with 32-bits bitstream readers.
  *
  *  Last operation is to close the bitStream.
  *  The function returns the final size of CStream in bytes.
  *  If data couldn't fit into `dstBuffer`, it will return a 0 ( == not storable)
  */
  
  /*-********************************************
  *  bitStream decoding API (read backward)
  **********************************************/
  typedef struct {
  	size_t bitContainer;
  	unsigned bitsConsumed;
  	const char *ptr;
  	const char *start;
  } BIT_DStream_t;
  
  typedef enum {
  	BIT_DStream_unfinished = 0,
  	BIT_DStream_endOfBuffer = 1,
  	BIT_DStream_completed = 2,
  	BIT_DStream_overflow = 3
  } BIT_DStream_status; /* result of BIT_reloadDStream() */
  /* 1,2,4,8 would be better for bitmap combinations, but slows down performance a bit ... :( */
  
  ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize);
  ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, unsigned nbBits);
  ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD);
  ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *bitD);
  
  /* Start by invoking BIT_initDStream().
  *  A chunk of the bitStream is then stored into a local register.
  *  Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
  *  You can then retrieve bitFields stored into the local register, **in reverse order**.
  *  Local register is explicitly reloaded from memory by the BIT_reloadDStream() method.
  *  A reload guarantee a minimum of ((8*sizeof(bitD->bitContainer))-7) bits when its result is BIT_DStream_unfinished.
  *  Otherwise, it can be less than that, so proceed accordingly.
  *  Checking if DStream has reached its end can be performed with BIT_endOfDStream().
  */
  
  /*-****************************************
  *  unsafe API
  ******************************************/
  ZSTD_STATIC void BIT_addBitsFast(BIT_CStream_t *bitC, size_t value, unsigned nbBits);
  /* faster, but works only if value is "clean", meaning all high bits above nbBits are 0 */
  
  ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC);
  /* unsafe version; does not check buffer overflow */
  
  ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, unsigned nbBits);
  /* faster, but works only if nbBits >= 1 */
  
  /*-**************************************************************
  *  Internal functions
  ****************************************************************/
  ZSTD_STATIC unsigned BIT_highbit32(register U32 val) { return 31 - __builtin_clz(val); }
  
  /*=====    Local Constants   =====*/
  static const unsigned BIT_mask[] = {0,       1,       3,       7,	0xF,      0x1F,     0x3F,     0x7F,      0xFF,
  				    0x1FF,   0x3FF,   0x7FF,   0xFFF,    0x1FFF,   0x3FFF,   0x7FFF,   0xFFFF,    0x1FFFF,
  				    0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF, 0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF}; /* up to 26 bits */
  
  /*-**************************************************************
  *  bitStream encoding
  ****************************************************************/
  /*! BIT_initCStream() :
   *  `dstCapacity` must be > sizeof(void*)
   *  @return : 0 if success,
  			  otherwise an error code (can be tested using ERR_isError() ) */
  ZSTD_STATIC size_t BIT_initCStream(BIT_CStream_t *bitC, void *startPtr, size_t dstCapacity)
  {
  	bitC->bitContainer = 0;
  	bitC->bitPos = 0;
  	bitC->startPtr = (char *)startPtr;
  	bitC->ptr = bitC->startPtr;
  	bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->ptr);
  	if (dstCapacity <= sizeof(bitC->ptr))
  		return ERROR(dstSize_tooSmall);
  	return 0;
  }
  
  /*! BIT_addBits() :
  	can add up to 26 bits into `bitC`.
  	Does not check for register overflow ! */
  ZSTD_STATIC void BIT_addBits(BIT_CStream_t *bitC, size_t value, unsigned nbBits)
  {
  	bitC->bitContainer |= (value & BIT_mask[nbBits]) << bitC->bitPos;
  	bitC->bitPos += nbBits;
  }
  
  /*! BIT_addBitsFast() :
   *  works only if `value` is _clean_, meaning all high bits above nbBits are 0 */
  ZSTD_STATIC void BIT_addBitsFast(BIT_CStream_t *bitC, size_t value, unsigned nbBits)
  {
  	bitC->bitContainer |= value << bitC->bitPos;
  	bitC->bitPos += nbBits;
  }
  
  /*! BIT_flushBitsFast() :
   *  unsafe version; does not check buffer overflow */
  ZSTD_STATIC void BIT_flushBitsFast(BIT_CStream_t *bitC)
  {
  	size_t const nbBytes = bitC->bitPos >> 3;
  	ZSTD_writeLEST(bitC->ptr, bitC->bitContainer);
  	bitC->ptr += nbBytes;
  	bitC->bitPos &= 7;
  	bitC->bitContainer >>= nbBytes * 8; /* if bitPos >= sizeof(bitContainer)*8 --> undefined behavior */
  }
  
  /*! BIT_flushBits() :
   *  safe version; check for buffer overflow, and prevents it.
   *  note : does not signal buffer overflow. This will be revealed later on using BIT_closeCStream() */
  ZSTD_STATIC void BIT_flushBits(BIT_CStream_t *bitC)
  {
  	size_t const nbBytes = bitC->bitPos >> 3;
  	ZSTD_writeLEST(bitC->ptr, bitC->bitContainer);
  	bitC->ptr += nbBytes;
  	if (bitC->ptr > bitC->endPtr)
  		bitC->ptr = bitC->endPtr;
  	bitC->bitPos &= 7;
  	bitC->bitContainer >>= nbBytes * 8; /* if bitPos >= sizeof(bitContainer)*8 --> undefined behavior */
  }
  
  /*! BIT_closeCStream() :
   *  @return : size of CStream, in bytes,
  			  or 0 if it could not fit into dstBuffer */
  ZSTD_STATIC size_t BIT_closeCStream(BIT_CStream_t *bitC)
  {
  	BIT_addBitsFast(bitC, 1, 1); /* endMark */
  	BIT_flushBits(bitC);
  
  	if (bitC->ptr >= bitC->endPtr)
  		return 0; /* doesn't fit within authorized budget : cancel */
  
  	return (bitC->ptr - bitC->startPtr) + (bitC->bitPos > 0);
  }
  
  /*-********************************************************
  * bitStream decoding
  **********************************************************/
  /*! BIT_initDStream() :
  *   Initialize a BIT_DStream_t.
  *   `bitD` : a pointer to an already allocated BIT_DStream_t structure.
  *   `srcSize` must be the *exact* size of the bitStream, in bytes.
  *   @return : size of stream (== srcSize) or an errorCode if a problem is detected
  */
  ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, size_t srcSize)
  {
  	if (srcSize < 1) {
  		memset(bitD, 0, sizeof(*bitD));
  		return ERROR(srcSize_wrong);
  	}
  
  	if (srcSize >= sizeof(bitD->bitContainer)) { /* normal case */
  		bitD->start = (const char *)srcBuffer;
  		bitD->ptr = (const char *)srcBuffer + srcSize - sizeof(bitD->bitContainer);
  		bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
  		{
  			BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
  			bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0; /* ensures bitsConsumed is always set */
  			if (lastByte == 0)
  				return ERROR(GENERIC); /* endMark not present */
  		}
  	} else {
  		bitD->start = (const char *)srcBuffer;
  		bitD->ptr = bitD->start;
  		bitD->bitContainer = *(const BYTE *)(bitD->start);
  		switch (srcSize) {
  		case 7: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[6]) << (sizeof(bitD->bitContainer) * 8 - 16);
  		case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
  		case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
  		case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
  		case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
  		case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
  		default:;
  		}
  		{
  			BYTE const lastByte = ((const BYTE *)srcBuffer)[srcSize - 1];
  			bitD->bitsConsumed = lastByte ? 8 - BIT_highbit32(lastByte) : 0;
  			if (lastByte == 0)
  				return ERROR(GENERIC); /* endMark not present */
  		}
  		bitD->bitsConsumed += (U32)(sizeof(bitD->bitContainer) - srcSize) * 8;
  	}
  
  	return srcSize;
  }
  
  ZSTD_STATIC size_t BIT_getUpperBits(size_t bitContainer, U32 const start) { return bitContainer >> start; }
  
  ZSTD_STATIC size_t BIT_getMiddleBits(size_t bitContainer, U32 const start, U32 const nbBits) { return (bitContainer >> start) & BIT_mask[nbBits]; }
  
  ZSTD_STATIC size_t BIT_getLowerBits(size_t bitContainer, U32 const nbBits) { return bitContainer & BIT_mask[nbBits]; }
  
  /*! BIT_lookBits() :
   *  Provides next n bits from local register.
   *  local register is not modified.
   *  On 32-bits, maxNbBits==24.
   *  On 64-bits, maxNbBits==56.
   *  @return : value extracted
   */
  ZSTD_STATIC size_t BIT_lookBits(const BIT_DStream_t *bitD, U32 nbBits)
  {
  	U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
  	return ((bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> 1) >> ((bitMask - nbBits) & bitMask);
  }
  
  /*! BIT_lookBitsFast() :
  *   unsafe version; only works only if nbBits >= 1 */
  ZSTD_STATIC size_t BIT_lookBitsFast(const BIT_DStream_t *bitD, U32 nbBits)
  {
  	U32 const bitMask = sizeof(bitD->bitContainer) * 8 - 1;
  	return (bitD->bitContainer << (bitD->bitsConsumed & bitMask)) >> (((bitMask + 1) - nbBits) & bitMask);
  }
  
  ZSTD_STATIC void BIT_skipBits(BIT_DStream_t *bitD, U32 nbBits) { bitD->bitsConsumed += nbBits; }
  
  /*! BIT_readBits() :
   *  Read (consume) next n bits from local register and update.
   *  Pay attention to not read more than nbBits contained into local register.
   *  @return : extracted value.
   */
  ZSTD_STATIC size_t BIT_readBits(BIT_DStream_t *bitD, U32 nbBits)
  {
  	size_t const value = BIT_lookBits(bitD, nbBits);
  	BIT_skipBits(bitD, nbBits);
  	return value;
  }
  
  /*! BIT_readBitsFast() :
  *   unsafe version; only works only if nbBits >= 1 */
  ZSTD_STATIC size_t BIT_readBitsFast(BIT_DStream_t *bitD, U32 nbBits)
  {
  	size_t const value = BIT_lookBitsFast(bitD, nbBits);
  	BIT_skipBits(bitD, nbBits);
  	return value;
  }
  
  /*! BIT_reloadDStream() :
  *   Refill `bitD` from buffer previously set in BIT_initDStream() .
  *   This function is safe, it guarantees it will not read beyond src buffer.
  *   @return : status of `BIT_DStream_t` internal register.
  			  if status == BIT_DStream_unfinished, internal register is filled with >= (sizeof(bitD->bitContainer)*8 - 7) bits */
  ZSTD_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t *bitD)
  {
  	if (bitD->bitsConsumed > (sizeof(bitD->bitContainer) * 8)) /* should not happen => corruption detected */
  		return BIT_DStream_overflow;
  
  	if (bitD->ptr >= bitD->start + sizeof(bitD->bitContainer)) {
  		bitD->ptr -= bitD->bitsConsumed >> 3;
  		bitD->bitsConsumed &= 7;
  		bitD->bitContainer = ZSTD_readLEST(bitD->ptr);
  		return BIT_DStream_unfinished;
  	}
  	if (bitD->ptr == bitD->start) {
  		if (bitD->bitsConsumed < sizeof(bitD->bitContainer) * 8)
  			return BIT_DStream_endOfBuffer;
  		return BIT_DStream_completed;
  	}
  	{
  		U32 nbBytes = bitD->bitsConsumed >> 3;
  		BIT_DStream_status result = BIT_DStream_unfinished;
  		if (bitD->ptr - nbBytes < bitD->start) {
  			nbBytes = (U32)(bitD->ptr - bitD->start); /* ptr > start */
  			result = BIT_DStream_endOfBuffer;
  		}
  		bitD->ptr -= nbBytes;
  		bitD->bitsConsumed -= nbBytes * 8;
  		bitD->bitContainer = ZSTD_readLEST(bitD->ptr); /* reminder : srcSize > sizeof(bitD) */
  		return result;
  	}
  }
  
  /*! BIT_endOfDStream() :
  *   @return Tells if DStream has exactly reached its end (all bits consumed).
  */
  ZSTD_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t *DStream)
  {
  	return ((DStream->ptr == DStream->start) && (DStream->bitsConsumed == sizeof(DStream->bitContainer) * 8));
  }
  
  #endif /* BITSTREAM_H_MODULE */
  